Breast cancer is one of the leading causes of morbidity and mortality for women in the United States. While several genes have been implicated in breast cancer, clearly there are additional as yet unidentified genes involved in the initiation and progression of these tumors. The primary objective of this proposal is to identify a gene on 17q25 which has been proposed to play a role in breast tumorigenesis. The specific aims of this plan are to 1.) define the critical region of 17q25 in breast tumors by loss of heterozygosity (LOH) analysis and localization of balanced translocation breakpoints from breast cancer cell lines; 2.) identify 17q25 candidate genes from the critical region and 3.) determine roles of candidate genes in normal tissue and breast tumors. Identification of this gene and elucidation of its role in normal cellular proliferation and breast carcinogenesis will aid in understanding the initiation and progression of this tumor and will provide a potentially powerful molecular tool for improving early diagnostic capabilities and effective treatment courses.